1. Field of the Invention
The invention relates to a processor and an energy saving method thereof, more particularly to a network processor and an energy saving method thereof.
2. Description of the Related Art
Many electronic devices, such as computers, storage media, printers, etc., are usually interconnected to form a network for conducting data exchange. Each network device establishes and maintains connections with other network devices through a network processor and a plurality of cables. For a network device that uses batteries as a source of power, battery power is rapidly exhausted when the network processor continuous to consume power even if there is no connection with other network devices. On the other hand, for a network device that does not use batteries as a power source, reducing energy consumption of the network processor can reduce the amount of heat dissipated thereby.
FIG. 1 illustrates a conventional network device disclosed in U.S. Pat. No. 6,993,667. The network device includes a physical layer 2. The physical layer 2 includes a physical layer circuit 21, an energy saving circuit 22, a receiver 23 and a transmitter 24. The physical layer 2 is operable between first and second energy saving modes.
Under the first energy saving mode, when the receiver 23 detects a connection activity, the energy saving circuit 22 powers up the physical layer 2 so as to establish and maintain connections with other network devices (not shown). Otherwise, the energy saving circuit 22 powers down components of the physical layer 2 other than the energy saving circuit 22 and the receiver 23.
Under the second energy saving mode, the energy saving circuit 22 periodically powers the transmitter 24 to generate a link pulse.
In this manner, the physical layer 2 is able to determine automatically whether energy consumption is to be saved based on the connection activity.
However, since the energy saving method involves shutting down power for the network device, a complicated energy saving circuit 22 is required to be designed to control switching between the energy saving modes. Moreover, a relatively long period is required to restore supply of power when powering up.
FIG. 2 illustrates another conventional network device that includes a RJ45 connection port 11, a network processor 12, and a south bridge 13. The RJ45 connection port 11 is able to detect plugging and unplugging activities of a cable (not shown) and to send a status signal to the south bridge 13. Based on the status signal, the south bridge 13 powers off the network processor 12 when the cable is unplugged from the RJ45 connection port 11, and powers on the network processor 12 when the cable is plugged into the RJ45 connection port 11. Energy consumption of the network processor 12 is saved accordingly.
However, the network device of FIG. 2 requires a specially designed RJ45 connection port 11 capable of detecting plugging and unplugging activities of a cable, which results in higher costs.